Cystic fibrosis (CF) is the most common early lethal genetic disease in Caucasians. CF leads to dysfunction in multiple organ systems, with progressive respiratory failure causing death in approximately 80% of patients. Lung transplantation is a treatment option for certain CF patients with end-stage lung disease. CF is currently the third most common indication for lung transplantation. Physicians follow guidelines to decide when to refer CF patients to lung transplant specialists. The guidelines are in part based on observational survival data from 1977-1989 that found a 2-year mortality of 50% in CF patients once their lung function worsened to a specific level (forced expiratory volume in one second (FEV1) less than 30% of the predicted value). There have been vast changes in the treatment of CF patients, predicted survival for CF patients, and the selection of lung transplant recipients in the past twenty-five years. Importantly, there have been no modern studies looking at survival of CF patients with low lung function (i.e. FEV1 <30%) in the US. Additionally, there have been no studies to evaluate outcomes for CF patients who forgo evaluation for lung transplantation beyond the timing recommended by the current guidelines. The overall study objective is to evaluate predictors and outcomes for patients with CF who receive guideline-inconsistent care in order to assess lung transplant referral guideline efficacy. The central hypothesis for the project is that the current lung function-based lung transplant referral guidelines do not reflect the improved health outcomes in the current CF population and may lead physicians to decide against referral of CF patients for lung transplant evaluation. This project addresses the central hypothesis and accomplishes the overall study objective by pursuing the following two specific aims: 1) Identify predictors of late referral and non-referral or lung transplant evaluation for a modern cohort of CF patients in the US Cystic Fibrosis Foundation Patient Registry (CFFPR) from 2006-2012; 2) Determine whether timely referral, late referral or non-referral of CF patients for lung transplant evaluation, using data from the CFFPR, is associated with survival from 2006 to 2012. An improved understanding of the population of CF patients who forgo guideline-consistent lung transplant evaluation could provide insight into whether the current referral guidelines require revision, or whether studies should focus on first determining patient factors related to non- referral and measures that might improve guideline adherence. Such results will have an important impact by providing potential targets for intervention if improved guideline adherence would be appropriate, or alternatively, by prompting the revision of current lung function-based guidelines if they are no longer identifying CF patients at the optimal time for lung transplant evaluation.